TC/Stabilitrak overly intrusive

[AC2024]

I am the OP for this thread. Coming back to it after a few months of experimenting and I think what I actually have been perceiving the e-diff "Working", not TC/stabilitrak. Considering I get the same feeling and behavior even with TC and stabillitrak completely turned off, I think it's the e-diff moving power all around.
My previous cars have only had helical ATBs (Wavetrack) which is reactive and smooth in lock up, so I suspect it's just my perception of the e-diff action.

So, I am a bit stumped as I continue to try to understand this. I spent some time with TC and stabilitrak completely off and in track mode with PTM set to Race 2. i still seem to get this weird hesitation which feels to me like TC cutting power (but note the light doesn't blink on the dash).

It seems to only happen in 2nd gear and in the 2-3RPM range. If I am mid corner and apply moderate throttle, I get the hesitation that you can hear (not real well) and see (on the Rev-counter - note how the revs kind of bounce up and down right at the transition to on throttle - that's what I am feeling). It feels like power being pulled and applied on and off a few times giving kick of a jerking sensation where my head will bump into the headrest a few times. In 1st gear, I'll get wheelspin and a bit of tail out (depending on PTM setting) but in second, I get this most of the time. Some of the time I'll feel the car rotate so incredibly perfectly, only for the next time to be this weird behavior again.

I attached a few short clips. Anyone have any thoughts? Is this just the normal e-diff? It certainly feels like in unsettle the car a bit, so I would be surprised.

By the way, sorry for the Paw Patrol - I'm a huge fan.

 

[MookdocOE]

So, I am a bit stumped as I continue to try to understand this. I spent some time with TC and stabilitrak completely off and in track mode with PTM set to Race 2. i still seem to get this weird hesitation which feels to me like TC cutting power (but note the light doesn't blink on the dash).

It seems to only happen in 2nd gear and in the 2-3RPM range. If I am mid corner and apply moderate throttle, I get the hesitation that you can hear (not real well) and see (on the Rev-counter - note how the revs kind of bounce up and down right at the transition to on throttle - that's what I am feeling). It feels like power being pulled and applied on and off a few times giving kick of a jerking sensation where my head will bump into the headrest a few times. In 1st gear, I'll get wheelspin and a bit of tail out (depending on PTM setting) but in second, I get this most of the time. Some of the time I'll feel the car rotate so incredibly perfectly, only for the next time to be this weird behavior again.

I attached a few short clips. Anyone have any thoughts? Is this just the normal e-diff? It certainly feels like in unsettle the car a bit, so I would be surprised.

By the way, sorry for the Paw Patrol - I'm a huge fan.

What are we looking at with these 3 sec clips?

 

[AC2024]

What are we looking at with these 3 sec clips?

Yea, i realize its a bit insane. If you look when power is applied youll see the rpms bounce a bit up and down and then smoothly increase. When thats happening i am feeling the power come in an out.

Reminds me of my old 328i with open diff and stiffened suspension and swaybars. When it was a bit cool for the summer rubber during a moderate acceleration out of a turn the inner wheel would lift enough to break traction at which point power would totally be cut for a moment by traction control.

 

[Champale]

I'm not sure how much the differential is even coming it to play at such low revs (i.e. out of the powerband). I have driven a 6sp 4BW and is felt superb with none of the herky jerky stuff you are describing and I was just in Sport mode when driving it. I was driving it a bit harder than what you show in those clips, though.

 

[Matt27]

I'm not sure how much the differential is even coming it to play at such low revs (i.e. out of the powerband). I have driven a 6sp 4BW and is felt superb with none of the herky jerky stuff you are describing and I was just in Sport mode when driving it. I was driving it a bit harder than what you show in those clips, though.

Agreed - doesn't look like you're anywhere near creating wheel spin at these revs and that cornering speed.

 

[AC2024]

Yea, agree-hence my confusion. I wish i ciuld articulate it better, but the hesitation is strange. Also, brings me to my other “complaint” (i love this car)-gearing is so tall. Both clips are admittedly low in rpm band as several have pointed out, but its 2nd gear-what else can i do?!?! These cars seem to be excessively tall geared and im not sure why.

Agreed - doesn't look like you're anywhere near creating wheel spin at these revs and that cornering speed

 

[rubberduck]

Yea, agree-hence my confusion. I wish i ciuld articulate it better, but the hesitation is strange. Also, brings me to my other “complaint” (i love this car)-gearing is so tall. Both clips are admittedly low in rpm band as several have pointed out, but its 2nd gear-what else can i do?!?! These cars seem to be excessively tall geared and im not sure why.

There must be a problem with one or more of the controllers. In my 5BW there are several sharp corners near my house that I hit at low speed in 2nd then give it about 1/2 throttle. The back slides out and some tire squeal, but power is smooth. When I do this in 1st it’s the same but with much more drama. This is either in Track/Dry or Track/Sport

 

[Matt27]

Yea, agree-hence my confusion. I wish i ciuld articulate it better, but the hesitation is strange. Also, brings me to my other “complaint” (i love this car)-gearing is so tall. Both clips are admittedly low in rpm band as several have pointed out, but its 2nd gear-what else can i do?!?! These cars seem to be excessively tall geared and im not sure why.

There's not really any way to slide around at low speeds with this much rubber at this power level.

Wet roads are better and you can have a ton of fun. Or I guess slap shitty tires on it.

Toyota famously put the Prius tires on the first gen 86 to get that result.

 

[Champale]

Yea, agree-hence my confusion. I wish i ciuld articulate it better, but the hesitation is strange. Also, brings me to my other “complaint” (i love this car)-gearing is so tall. Both clips are admittedly low in rpm band as several have pointed out, but its 2nd gear-what else can i do?!?! These cars seem to be excessively tall geared and im not sure why.

That's funny - when I drove the 4BW I thought to myself how nice and short the gears were compared to my 5BW 6sp. I haven't seen a 'speed in gear' chart for the 4BW but they felt appropriate to me (and I love short gearing in other cars I've owned).

 

[AC2024]

That's funny - when I drove the 4BW I thought to myself how nice and short the gears were compared to my 5BW 6sp. I haven't seen a 'speed in gear' chart for the 4BW but they felt appropriate to me (and I love short gearing in other cars I've owned).

Interesting. I just checked the gear ratios and the 4 is considerably taller geared than my f30 335 6mt. With the 5, it helps to have 600+ tqs that come on lower. The 4 doesnt make peak torque until 3500rpm and then “only” makes 455 tqs, which sure is still a lot compared to alot of cars, but not 600+ lol

 

[Champale]

I'm wondering if the feeling you are noticing is the engine being unhappy because it's being lugged. Does it do the herky jerky thing above 4k rpm?

 

[MookdocOE]

I'm wondering if the feeling you are noticing is the engine being unhappy because it's being lugged. Does it do the herky jerky thing above 4k rpm?

It's 4 and not supercharged typical Turbo lag even more noticeable around corners? Not a turbo I haven't driven as of late without that on abrupt turns?

 

[BimmerFan]

Interesting. I just checked the gear ratios and the 4 is considerably taller geared than my f30 335 6mt.

Everything is geared taller than a manual BMW.

 

[AC2024]

Everything is geared taller than a manual BMW.

Haha! Well put. Glad I still have it - it's a nice variety between the BM and BW.

 

[AC2024]

I'm wondering if the feeling you are noticing is the engine being unhappy because it's being lugged. Does it do the herky jerky thing above 4k rpm?

I get it but I don't get it. A car in 2nd gear >2K rpm isnt being lugged. I am not sure what the alternative is - downshift to 1st >20 mph? The torque multiple in 2nd gear should enable standing on the throttle from 2K rpm with no lugging. I also wouldn't describe the behavior as lugging - it's more synthetic

That said, I suspect you're right in that the engine just doesn't love being low in the revs.

 

[Champale]

To me, 2k rpm is lugging a smallish displacement turbo engine in a 3800+lb car.

 

[rubberduck]

I thought 2K was lugging my LT4. Guess it’s all perspective. I use 2.5K as the low limit for everyday cruising.

 

[AC2024]

I thought 2K was lugging my LT4. Guess it’s all perspective. I use 2.5K as the low limit for everyday cruising.

don't get me wrong - i typically keep the engine spinning 3-4K RPM to stay in the poweband. However, it's a somewhat unique circumstance in slower driving. 2nd gear at 20 mph is ~2K RPM. I am not going to shift into 1st gear driving down the road.

There is also a difference between lugging and running the engine below peak torque.

 

[DCV]

Why not use 1st gear when “driving down the road”? Note that the 4 BW manual has titanium rods, that helps the engine spin up quickly but also carrys less momentum. On those sharp low speed turns use 1st gear, it’s ok.

 

[rubberduck]

don't get me wrong - i typically keep the engine spinning 3-4K RPM to stay in the poweband. However, it's a somewhat unique circumstance in slower driving. 2nd gear at 20 mph is ~2K RPM. I am not going to shift into 1st gear driving down the road.

There is also a difference between lugging and running the engine below peak torque.

I agree that an LT4 at 2K in 2nd can get up ok. Just not ideal acceleration profile.